Aspinall Unit operations update: Gunnison Tunnel diversions ending for season

From email from Reclamation (Erik Knight):

On Wednesday, November 1st, diversions to the Gunnison Tunnel will end for the season. Releases from the Aspinall Unit will be adjusted in coordination with the ramp down schedule for Gunnison Tunnel diversions in order to keep Gunnison River flows near the current level of 750 cfs. There could be fluctuations in the river throughout the day until the Gunnison Tunnel is completely shut down.

On Thursday and Friday, November 2nd and 3rd, releases from the Aspinall Unit will be reduced to 300 cfs during the day time hours in order to allow for completion of the sonar survey of the Crystal Dam stilling basin. Gunnison River flows will drop down towards 300 cfs during the day while returning to 750 cfs during the non-working hours. After the sonar survey is completed at the end of the day on November 3rd, river flows will return to the current level of 750 cfs.

Flows in the lower Gunnison River are currently above the baseflow target of 1050 cfs. River flows are expected to stay above the baseflow target for the foreseeable future.

Pursuant to the Aspinall Unit Operations Record of Decision (ROD), the baseflow target in the lower Gunnison River, as measured at the Whitewater gage, is 1050 cfs for October through December.

Currently, diversions into the Gunnison Tunnel are near 850 cfs and flows in the Gunnison River through the Black Canyon are around 750 cfs. After the shutdown of the Gunnison Tunnel and completion of the Crystal stilling basin sonar survey, flows in the Gunnison River through the Black Canyon will return to 750 cfs. Current flow information is obtained from provisional data that may undergo revision subsequent to review.

Aspinall Unit operations update: Lower Gunnison streamflow above baseflow target

Fog-filled Black Canyon via the National Park Service

From email from Reclamation (Erik Knight):

Releases from the Aspinall Unit will be decreased by 100 cfs on Thursday, October 12th. Diversions to the Gunnison Tunnel will be reduced by 100 cfs on Wednesday, October 11th so there will be a short period of flows over 1000 cfs in the Gunnison River through the Black Canyon before the river returns to a flow of 950 cfs by late Thursday morning.

Flows in the lower Gunnison River are currently above the baseflow target of 1050 cfs. River flows are expected to stay above the baseflow target for the foreseeable future.

Pursuant to the Aspinall Unit Operations Record of Decision (ROD), the baseflow target in the lower Gunnison River, as measured at the Whitewater gage, is 1050 cfs for October through December.

Currently, diversions into the Gunnison Tunnel are near 975 cfs and flows in the Gunnison River through the Black Canyon are around 950 cfs. After this release change Gunnison Tunnel diversions will be about 900 cfs and flows in the Gunnison River through the Black Canyon will still be around 950 cfs. Current flow information is obtained from provisional data that may undergo revision subsequent to review.

@USBR needs to draw down Blue Mesa to meet winter target, water for Lake Powell

From The Grand Junction Daily Sentinel (Gary Harmon):

Blue Mesa this week was brimming at 99 percent full and it was far from alone among Colorado River Basin reservoirs.

Morrow Point and Crystal reservoirs below Blue Mesa on the Gunnison River were 96 percent and 90 percent full, respectively.

“It’s going to take a lot of work” to reduce Blue Mesa’s level to 70 percent of full, or 580,000 acre-feet of water, U.S. Bureau of Reclamation hydrologist Eric Knight said Thursday.

Typically, all three reservoirs are well depleted by this time of year to meet irrigation demand, as well as feeding more water into Lake Powell, the largest storage unit in the Upper Colorado River Basin.

This year, however, river managers learned late that there was more snow in the high Colorado mountains than they had believed when deciding how much water to release early on this spring, officials said during a regular update on management of the Aspinall unit.

Several factors contributed to the underestimation of snowpack, not least of them the warm March in the Colorado Rockies and the fact that some snow-monitoring gauges were covered with snow, incapable of providing accurate information, officials said.

Recent storms in the high country also have pumped more water into the reservoirs.

River managers have to balance the need to release more water out of the Aspinall unit with making sure that the Gunnison doesn’t overflow its banks in Delta.

At the same time, managers also have to get as much water as possible into Lake Powell, which can hold some 24 million acre-feet of water but which now holds about 15.2 million acre-feet.

The Bureau of Reclamation this year is to release 9 million acre-feet of water into Lake Mead.

Aspinall Unit operations update: 1150 CFS in Black Canyon

Fog-filled Black Canyon via the National Park Service

From email from Reclamation (Erik Knight):

The spring peak operation has officially concluded. Due to an issue with the power plant at Crystal Dam, the ramp down was forced to end prematurely. As of today releases are being made through the bypass gates at a rate of 2150 cfs. This has put flows in the Gunnison River through the Black Canyon around 1150 cfs. This release rate is expected to continue for the foreseeable future. Further adjustments to this release rate may be necessary to manage the remaining runoff coming into Blue Mesa Reservoir.

Aspinall Unit operations update: 4,500 cfs in Black Canyon — @USBR

Sunrise Black Canyon via Bob Berwyn

From email from Reclamation (Erik Knight):

The spring peak operation is nearing completion. Releases are currently being made to sustain half bankfull flow levels at the Whitewater gage, as well as to manage the forecasted runoff into Blue Mesa Reservoir. Releases from the Aspinall Unit have been around 5,500 cfs during the past week and that release rate will continue through Sunday, June 11th. Flows in the Gunnison River through the Black Canyon are currently around 4,500 cfs and can be expected to stay near this level through Sunday, June 11th. Starting on Monday, June 12th flows will begin to ramp down towards the summertime release level. This should result in flows in the Gunnison River through the Black Canyon around 900 cfs to 1,000 cfs once the ramp down is completed on Monday, June 19th.

Aspinall Unit operations update

Aspinall Unit dams

From email from Reclamation (Erik Knight):

The May 15th forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 825,000 acre-feet. This is 122% of the 30 year average. Blue Mesa Reservoir current content is 681,000 acre-feet which is 82% of full. Current elevation is 7502.4 ft. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 ft.

Based on the May 1st forecast, the Black Canyon Water Right peak flow target is listed below:

Black Canyon Water Right

The peak flow target is equal to 6,427 cfs for a duration of 24 hours.

The shoulder flow target is 831 cfs, for the period between May 1 and July 25.

The May 15th forecast of 825,000 af is now in the Average Wet category and the Aspinall Unit ROD flow targets have changed. Based on the May 15th forecast, the flow targets are listed below:

Aspinall Unit Operations ROD

The year type is currently classified as Average Wet.

The peak flow target is 14,040 cfs and the duration target at this flow is 2 days.

The half bank-full target is 8,070 cfs and the duration target at this flow is 20 days.

The spring peak operation has reached peak release level. The release increase made this morning, May 24th, should result in the first day of flows > 14,000 cfs at the Whitewater gage, arriving by the afternoon of May 25th. Today, flows in the Gunnison River through the Black Canyon have reached 11,500 cfs. The current rate of release is planned to continue through Sunday, May 28th. At this time it is projected that there is additional water that needs to be released from the Aspinall Unit to prevent overfilling at Blue Mesa Reservoir, therefore the peak release is continuing to meet more than the 2 day duration target.

@USBR Increases Releases from the Aspinall Unit to Meet Flow Targets on the Gunnison River

Black Canyon of the Gunnison

Here’s the release from the US Bureau of Reclamation (Justyn Liff/Erik Knight):

The Bureau of Reclamation began increasing releases from the Aspinall Unit, consisting of Blue Mesa, Morrow Point, and Crystal reservoirs on the Gunnison River, on May 14, 2017. The increased release will attempt to meet flow targets on the Gunnison River, designed to benefit endangered fish species downstream while continuing to meet the congressionally authorized purposes of the Aspinall Unit.

Flows in the Gunnison River through the Black Canyon will increase at a minimum of 500 cubic-feet-per-second a day resulting in flows through the canyon that may reach 12,000 cfs by approximately May 23. Flows will remain around 11,500 cfs to 12,000 cfs for 3-5 days before incrementally decreasing toward a range of 5,000 cfs to 5,500 cfs around May 29.